Process for regeneration of spent doctor solutions



R. M. LOVE July 29, 1952 PROCESS FOR REGENERATION OF' SPENT DOCTOR SOLUTIONS Filed MarOh l5. 1948 Patented July 29, 1952 "PROCESS" FOR REGENERATIONv OF SPENT e DOCTOR SOLUTIONS. Robert M. Love, Baytown, Tex. assigner, by

mesne assignments, to Standard Oil Development Company, Elizabeth, N'. J '.,v acorporation 'ot'Delaware AnplieationMarch. 13, 1948, scifi-alim 14,634

l This. invention is concernedfvwith amethod of improving, theA regeneration of: spent doctor solutions. `Morespecifically, it .concerns a. method for increasing. the rate; ofl regeneration. of doctor solutions spent, in theftreatment ofr mercaptanbearing-oils.

It is4 well. known-.tosvveeten either virgin naphthas produced .by thefcatalytic or thermal cracking of virginhydrocarbon oils which contain obnoxious mercaptans, by treatment of such materials with. al doctor, solution; (an alkali .metal plum-bite), and. withfelement sulfur.V In order to eliminate excessive, ,lossof :costly lead' compounds, the. spentA doctorso1ution,., which comprises lead lsuldes.efomied duringv the sweetening step and entrainednaphthais vregenerated for reuse in the` sweetening.V cycle;. Thispis vusually accomplished'by'blowing theispentdoctor solution with air-.or otheroxidizingvmedium. Quite frequently, whengtheieguipmentemployedin the-doctor, sweetening; process -sbeing,(operatedV atfmaximum oapacity,. such .larga `quantities of ,spentdoctor solution are producedY that either considerable time;f required to. carry out the regeneration stepf or there s-notr sucient. capacity in the regeneration equipment to `handle all of. the spent solution. Consequently., large quantities ofV the spent solutionrmust-either.be. discarded or stored for long-J periodsiofftime... Igtwould bev extremely desirable; therefore-torina a. procedure for increasing thefr-ateat which g spent doctor solutions caribe-regenerated.' y

It,l is;4 known that; manyV virgin and.. all. cracked naph-thas7.colritaingv oleiinioconstituents. There. is very good,reason.l to believe. that some of-.theolefins present.: int-suchRaph.thasj are carried along withsnent.. peter: solution: to. the" .regeneration operation. Duringthe air-treating operation these-olefin@ bodies evidently arefpolymer-ized o1' oxidized to;v polrmelssand.; gumsziwhioh tend; to depositv on. rthegpartieles. of.. -leadysulfite asA the naphtha-is evaporatedfromtheslurry during-.the fnxidationvv step. The deposition oft suchmaterials on. the leadsuldea particles is believed; toa-result in the formationfof-'a-visceus; gummyliilmwrhich interferesl with theqliiiusionfoflead psulde; and,

.eterds the: oxidation. ofthis .material l to `solupblef-,lead .-compounds;l L, have y found sturm). duties fihedfresenerationstee ineneasesthe that maintaining; crematie.- .i1-.vd.rocariwris1 in thel '12.o1aims. (o1. 2,3--59 Cil regeneration rate. g This probably because. the gummy bodies are kept ,ini solution .which makes it. possible Yto obtain eieient contactbetween. the oxygen and lead sulfide particles. I. have found a simple andinexpensive procedure for accomplishing'. the accelerated. regeneration of. such solutions.

It is, therefore.. thechiei'objeet of? the present invention to provide.. ameans'` of,` carrying. outY the accelerated regeneration. of doctor solutions spent inthefsweejtening .of sour. naphthas.'

Other objects. of.- the. present .invention will be.- come apparent from a reading of'the following descriptionand. claims. ofmy invention.

Brieeathe. presenti invention comprises. washing. a Spent.. doctor. solution. with an aromati'ctype hydrocarbon solvent. settling. the Washed material to separate y21.,.111ajorv portion. of( the aromatic. solventfrom the spent'solution arid contactin'g the. spent washed; doctori'solution/Icontainingl a minor portion'of. aromatic, solvent with av freeoxygen containing' gasat. an. elevated temperature.. to fo'rmpregenerated. doctor solution. If desired, theywlasliing; step.. may; bey eliminated and aromatics'. may.. bek added"y o, lthe .spenti solution beforeregeneraton.. The'. regeneration, operationm'ay be caniednutetner' on the. .total Spent doctor. solution.. or on. the. slurry: layerv lobtained by settling'the spent doctocsolution.

In. .order to, describe. more .completely one method'. of carrying; out'. my invention, yreference is..mad'eto theV sole ligure. in the. form. oi`.a..iiow diagram illustrating several embodiments there.- eig..

'Ilurnin'g novi` to` the;` drawing; the'.i numeral. I .I

designates ai. line through., which is. numped d0etor solutionV received from. va conventional, 'treatingzone notshown,z '.Ihi'ssolution.will havebeen formedby treatment. of. a. niercaptan-'bearing oil With, ireshior. regenerated doctor solution .con-- tfaining. appreciable quantities.. of soluble; lead. and with elemental sulfur. The solutionisseparated fromthesweetened napl'itlfia.y Appreciablequan.- titiesof lead suldesvvilllbe present therein. The solution containing. thefleadsuldesis Withdrawn frQm the .011 and Pumped.- through-.lnea l'l;...i1.1t0 Settling. .tanklz2f wherein .it is Settled intoV` .three laver-s; as ton f layenwhieh- .comprises naphthav and which is weithdra t1-irene.

. Y mei-1153,.. aamilddle .Slllfzly :..Orn emulsio f. laver containing .the.bn1.k of

3 the lead sulfide precipitate emulsied with oil and caustic which is withdrawn through line I4 containing pump I5 and valve I6, and a bottom layer of caustic containing a small amount of dissolved lead which is withdrawn through line I'I containing valve I8. The middle slurry layer is charged into washing zone I9 into which extends an agitating means 20 connected to shaft 2I and rotated by prime mover 22.

Storage vessel 23 contains anl aromatiovnaphtha containing over about 50 per cent aromatics. A portion'ofr thisna'phtha is withdrawn through line 24 containing pump 25 and is charged into washing zone I9 wherein the slurry and aromatic naphtha are thoroughly mixedwby means of stirring device 20. After the materials have been thoroughly contacted, the stirring operation is discontinued and the contents of the washingV zone are allowed to settle. Aromatic naphtha is withdrawn as a top layer from zone I9 through line 2B containing pump 21 and is charged, ifA desired, into distillation zone 28 containing heating means 29. In this distillation operation, high boiling gums and polymers removed from the slurry in washing zone I9 and dissolved in the aromatic naphtha arey removed as' a high boiling fraction 'throughfline 30. y Aromatic naphtha substantially freeY of thehigh boiling gums and polymers 'isrwithdrawn Vthrough line 3l containing pump'32 and is subsequently passed to storage tank 23'. The washed slurry layer settling in the bottom `of .tank I9 is withdrawn through line33 containing pump 34 and is passed to a regeneration zone such as tank 35. If desired, a small amount of aromatic naphtha may be added to ,the withdrawn slurry by lines 24 and 36 and blendedV with the slurry passing through line33'. iv y' The WashedV slurry containing a minor` portion of aromatic naphtha is 'then contacted with a free oxygen containing gas such as air which is introduced into tank 35 through line 46 and distributing'devioer. The contents of tank 35 may beheated, if desired, by heating means 38 which miayjsuitably compriseasteam c oil.j :It is"usually preferable to', maintain the temperature ofthe `materialbeing regenerated at a temperature *of Yfrom about atmospheric to 350 F. in order to' obtain the most' efficient, regeneration rate. Aftertheair-blowing operation has continued for ar period of several hours, substantially all of -thelead sulfidesjinv the doctor solution are converted to soluble lead compounds such as lead oxide and lead thiosulfate.

If desired, lan alkali metal hydroxide solution may be Vadded to the'wa'shed slurry before the regeneration step. This'may be accomplished by introducing an aqueous alkaline solution through line 4'I and combining it with the washed slurry passing through line. 33 linto regeneration zone 35.

The .regenerated solution is then vwithdrawn from the tank 35 through line 39jcontaining pump. 40 and is routed to solution zone 4I. The clear' spent doctor solution withdrawn by line .I1 from 'settling tank 12 may be mixed withl the regenerated doctor solution and the-combined stream passed to solution zone 4I. A free oxygen-containing gas, such as air, is then passed throughline 42 and distributing means 43 into zone IIIV such that the contents thereof may be agitated'to cause solution of oxidized lead salts in the* mixture and to oxidizefany-lead suldes remainir'ig in the combined Streams. If desired,

means of line 44. The regenerated doctor solul tion may then be withdrawn from` zone 4I' through line 45 and passed to the sweetening zone, not shown.

If desired, the washing operation may be carried out by washing the total spent doctor solution passing through line I I with aromatic naphtha without carrying out the intermediate settling operation. This procedure is not always desirable since, very large Avolumeslofspent solution mu'st Atheir-be passed totheregeneration zone for contacting with l"the free oxygen-containing gas. Under some conditions, however, the settling operation may not be desired and eiiicient results may be obtained Without including this particular step. The washing step may be carried out in several mixing zones or in a countercurrent treating tower wherein slurry is introduced at the top and naphtha is introduced additional' alkali j metal hydroxide solution may y be added tothe contents of solution tanklll by at the bottom ofthe tower and the materials passed through ei'l'icient contacting means such as bell cap trays or the like.

Another modification of my invention which is preferred in some operations where a preliminary washing step is not required comprises passing slurry through-1ines`I'4, 48 and 33 directly to regeneration zone 35. Aromatic naphtha-is added by wayfof line'36 to theslurry passing through line-33.l A substantial volume of naphtha is added to provide from about 2 to 40% by volume of aromatic hydrocarbons based on the naphthaslurry mixture. The total spent reagent may also be passed directly from line I Ito line 48 without the intermediate settling'operation and aromatics added as described above. 1

In lsome casesit may be desirable-to remove the aromatic 'naphtha from the regenerated doctor'solution before-it is recycled to the sweetening process. This 'may be accomplished conveniently by'steam distilling the regenerated solution withdrawn throug'hlline 39 from regeneration zone 35. -In 'other cases itmay be desired to steam' distill 1 the` i washed slurry f withdrawn from washing-"zone I9. y If this steam distillation -op'- eration-is`carried`,out,-however, it will be necessary to add aromaticv lri'a'ph'tha to the steam distilled slurry before 'it 'is passed to regeneration zone35.'

rThe beneficial results to be obtained from the practice'y of my inventionwih now bedescribed in conjunction with various examples. Mercaptan-bearingfnaphthas boiling from about F. to 450 F., having copper numbers in the range of l0 to 25, and having olefin contents of about 15-volume percent were'contacted with doctor solutions having 'soluble leadcotents of from 0.05 to 0 .20 pound per gallon `and with suilicientV sulfur to breakout lead suldes from the treated solution.r The spentdo'ctor solutions Vwithdrawn from the sweetening process having soluble lead contents of substantially zero pound of lead per gallon` of doctor solution were'then settled for a periodr of abou'tfounhours. The middle slurry or emulsionlayer withdrawn from the settled product waslthen'pretreated under various conditions and' regeneratedv with constant' amounts of airat aj temperaturel of F. I n each'case analyses were" obtained Vat definite periods on the doctor solution` undergoing the oxidation treatment in orderto/ determinev whenl the vformation of soluble lead in the regenerated' mixture was substantially .i complete. f The time,v Y required to regenerate each slurry wasthen used'in calculating the regeneration ra'tewhich is reported as pound of lead/oxide per vgallonofslu'rry treated vper hour".

Ineach ease a blank run wasmade in-gwhich untreated slurry*l was oxidized' vvunder constant con'- ditions. The pretreatment operations included washing the slurry` beforeregeneration with a para-inic lnaphthaboiling from VVabout' 100 to 200 F., with an aromatic naphtha boilingY from 325 to 550' F l or,`-With toluene, steam distilling the slurry, or ysteam distillingthe slurry followed by adding a small amount of aromatic' naphtha before oxidation'. 10

Theresults of these various runs areshown in the following table:

` ticeof my invention preferably-.should contain Slurry" Employed Y A Pretreatment 'of YLead' Blurty:

NaphthaWash EmployedV l. .1 i Vo1..pereent based on slurry Slurry Steam Distilled l Aromaticnaphtha added tosteam distilled slurry,r ol. percent.-.-

Regeneration o1' Slutty:

Naphtha remaining in slurry, Y j f Vol. p ercent 0. I0 20 Aromatics remalningfin. slurry, f VOL percent; Y Y Regeneration rate, Poundof lead/ gallonv of slurry per h0ur Increaseviu regenerationrate, per n cent '25` Pound leadregenemted per gallonv of slurry during regeneration period 2 Naphtha 0 v 100 3 Naphthaf 0 100 None Yes

' 1 'H'Naphtha 0L 10 l Slurry washed with naphtha, the mixture settled and the'slurry was thenvseparated fr ornnaphtha. 2 Paraflinic naphtlia` containing 10 volume percent aromatics and boiling in therange of l00fto 200 F. Aromatic naphtha containing 85 volume percent aromatics and bollinginthesrange of 325 to 550.I F.

It will be noted that washing .the slurry before regeneration. with 100%Y volume of parafnic naphtha resulted in very littlec improvement in the regeneration rate. It is also noted that steam resulted inno improvement in the regeneration rate, Washing the` slurry with'as little as 10% volume of' kerosene extract, withdrawing the major portion of the extract and oxidizing the slurry containing 3.4% by volume offaromatic hydrocarbons increased the regeneration rate aboutr 100% over that' obtained when no pretreatment operation was employed. Washing the slurry with 100% by Volume of eitherY high boiling aromatic naphtha or toluene and then regenerating the slurries containing 15 and 20 volume. perl cent aromatic hydrocarbons, respectively, resulted in increasing the regeneration rate appreciably as compared to that obtained whenv no pretreatment Awas employed'. Steam 50 distillation of the slurry followed .byadding .about one volume. percent oi aromaticv hydrocarbons.. increased the regeneration rate-'very slightly.

The amount of aromaticsmantained in the spent doctorr solution. during' regeneration. will depend to some extent on the type of hydro"- carbonv o'il originally sweetened. lioi:` example, sweeteningA virgin naphthas; containing only smallV quantities (below 1%.) of oleiins will'. result 60 in a spent reagent which may be effectively re.- generated when containing only about 2 to 5% aromatic hydrocarbons. Spent reagents from sweetening operations on cracked distillates containing 10% and' higher concentrations of olens 65 hydrocarbons need to be present as a ruleA during the.` regeneration step than is the case WhereA4 the Washing step is eliminated and aromatics are added directly to the reagent or slurry before the air blowing step. f f

The aromatic wash naphtha used. in the pracveniently by extracting an aromatic-containing naphthau with' liquid sulfur dioxlitle'I at reduced vtemperatures to form anextractphas'e, removing y i F- SO2 from the extract phase and recoveringl the distillation. of the slurry prior toY regeneration 30 about 250 F; and preferalzxly shouldboil from about 300 to 550 to 600fl'.;Naphthas` boiling below aboutf250 F.,.such. as benzene;l and toluene, volatil-ize rapidly from the:l slurryY duringV the re generation. step. carried. out' at. elevated temperature and. atmospheric pressure; consequently, they." cannoti-act. as; asolventsfor: the gum-forming bodies during this/particular operation.. If the areblowing; operation. isscarried. out in pressure K equipment such that the operating-pressuresmay be asl highas.: 100. toI 20.0 `pounds per square inch, the lighter aromatic; solvents. suchas toluene or benzene maybe present in the material being regenerated even: atV temperatures as high as 300 E. Straight runlight petroleum distillates oi low; aromatic content. are-.usually` undesirable for usein the. practice. of: my invention because suliicient aromatic hydrocarbons '.do,y not remain. in the` regenerating slurry to:,act.as effective solventsduringthe regenerationstep.

Inthe-appendedclaims;A thefterms-spentalkali metalv plumbite solution and alkali metal solutions separated from the bulk of the treated oil. m

I do not intend to be limited toany theory as to the mode-by which improved results are obtained in my invention. The regeneration of any spentfalkali metal plumbite solution in the presence of aromatic hydrocarbons will fall within the spirit and scope of the disclosures given in this specification and following claims.

The nature and objects of the present invention having been fully, described 4and illustrated, what I wish to claim as new and useful and to secure by Letters Patent is:

1. A method for regenerating spent alkali metal plumbite solution which includes the steps of adding to said solution a liquid hydrocarbon phase comprising a major portion of aromatic hydrocarbon in an amount suicient to dissolve substantially all polymers and gums formed therein,

and contacting said solution with a free oxygencontaining gas in the presence of said added liquid.

2. A method for regenerating spent alkali metal plumbite solution whichcomprises washing` the spent solution with an aromatic hydrocarbon solvent boiling above about 175 F., removing a portion of saidsolvent from the spent solution, contacting said solution in the presence of about 2% to about 40% by volume of said aromatic hydrocarbon solvent with a free oxygen-containing gas under conditions adapted to maintain said hydrocarbon solvent in liquid phase, and recovering a regenerated plumbite solution suitable for sweetening mercaptan-bearing hydrocarbons.

3. A method for regenerating alkali metal plumbite solutions yspent in the sweetening of mercaptan-bearing oils which includes the steps of separating a slurry layer comprising lead sulfide, alkali metal hydroxide solution, and oil from the spent solution, adding to said slurry an aros matic hydrocarbon solvent boiling in the range between about 175 and about 550 F. in an amount ranging from about 2% to about 40% by volume, contacting said slurry and said solvent with a free oxygen-containing gas under conditions adapted to maintain saidV solvent in liquidv phase, and recovering a solution suitable for sweetening mercaptan-bearing oils. Y'

4. A method for regenerating alkali metal plumbite solutions spent in the sweetening of mercaptan-bearing oils which comprises the steps of forming an admixture comprising a major portion of said spent solution and from about 2% to about 40% by volume of an aromatic hydrocarbon solvent boiling within the range between I 550 F., agitating said solvent with said reagent 1 to remove gum-forming materials therefrom, separating a portion ofthe solvent from resulting washed reagent, passing to said regeneration zone washed reagent containing from about 2% to 8 about 40% by volume of said aromatic hydrocarbon solvent, and maintaining saidV solvent in liquid phase during contacting with said gas.

6. In a 'method for oxidizing leadsuldes in alkaline metal plumbite solutions spent in sweetening-.mercaptan-bearing oilsto soluble lead salts Which Vincludes the step of contacting the lead suldes with free oxygen-containing gas, the improvement which comprises admixing with said lead sulfldes a solvent comprising a major portion of liquid aromatic hydrocarbons andmaintaining in liquid phase in the presence of said lead sulfides during said contacting step an amount of said solvent suncient to dissolve substantially all polymers and gums formed therein.

7. A method for oxidizing lead suldes in alkali metal plumbite solutions spent in the sweetening of mercaptan-bearing oils to soluble lead salts which comprises the steps of 'settling said spent solution, separating a slurry comprising. lead sulde and an alkali metal hydroxide solution from said spent solution, washing said slurry with an aromatic hydrocarbon solvent boiling within the range between about 175 F. vand about 550 F., separating a washed slurry containing from about 2% to about 40% by volume of said solvent, and contacting said slurry,and said solvent with a free oxygen-containing gas under conditions adapted to maintain said solventin liquid phase to vcon- `vert lead suliides to soluble lead salts.

8. In the regeneration of alkali metal plumbite solutions spent in the sweetening of mercaptanb-earing oils which includes the steps of separating a slurry comprising lead sulfide and an alkali metal hydroxide solution from said spent solution and contacting said slurry with a free oxygencontaining gasrfor a period of time suflicient to convert lead suldes to soluble lead compounds, the improvement which comprises agitating said slurry with an aromatic hydrocarbon solvent boiling above about 175 F., separating a washed slurry-aromatic hydrocarbon solvent mixture containing aromatics in the range of 2% to 40% by volume based on the total mixture, charging said slurry-aromatic hydrocarbon mixturetolsaid regeneration step, and maintaining said aromatic hydrocarbon solvent in liquid Yphase during contacting with said gas.

9. A method in accordance withV claim 8 in which the aromatic hydrocarbon-solvent contains at least 50% aromatcs.

10. A method in accordance with claim 8 in which the aromatic hydrocarbon solvent is benzene.

11. A method in accordance with claim 8 in which the aromatic hydrocarbon solvent is toluene.

` l2. A method in accordance with claim 8 in which the aromatic hydrocarbon solventV is Van cmatic naphtha boiling between 325 F. and

ROBERT M. LOVE.

REFERENCES CTED The following references are of record in the le of this patent:

UNITED STATES PATENTS (Other references on following page) y OTHER REFERENCES Ott and Reid, Reactions of Some Mercaptans 10 with Alkaline Sodium Plumbite Solutions, Ind. 

1. A METHOD FOR REGENERATING SPENT ALKALI METAL PLUMBITE SOLUTION WHICH INCLUDES THE STEPS OF ADDING TO SAID SOLUTION A LIQUID HYDROCARBON PHASE COMPRISING A MAJOR PORTION OF AROMATIC HYDROCARBON IN AN AMOUNT SUFFICIENT TO DISSOLVE SUBSTANTIALLY ALL POLYMERS AND GUMS FORMED THEREIN, AND CONTACTING SAID SOLUTION WITH A FREE OXYGEN- 